Anthropogenic impacts on the properties and the distribution of the terrestrial biogenic silica pool.

Date: 26 April 2018

Venue: Campus Drie Eiken, S.001 - Universiteitsplein 1 - 2610 Antwerpen-Wilrijk (route: UAntwerpen, Campus Drie Eiken)

Time: 10:00 AM

Organization / co-organization: Department of Biology

PhD candidate: Dácil Unzué-Belmonte

Principal investigator: Patrick Meire & Eric Struyf

Short description: Public defence of the PhD thesis of Mrs. Dácil Unzué-Belmonte - Faculty of Science - Department of Biology


The terrestrial Si-cycle has received increased attention in the past two decades. Multiple studies show several processes involved: interactions among primary lithology and weathering, biotic Si uptake, formation of secondary pedogenic phases and environmental controls such as precipitation, temperature and hydrology. Plants take up dissolved Si (DSi) from soil water, forming protective structures called phytoliths, often referred to as biogenic silica (BSi). The presence of phytoliths confers some benefits for the plant like resistance against herbivores or stress alleviation (Epstein, 1994). The solubility of BSi in soils is higher than other pedogenic Si phases which results in an active plant-soil Si turnover that controls the terrestrial Si-filter (Struyf and Conley, 2009). The importance of characterize and quantify the BSi pool in soils is thus important in order to better understand the terrestrial Si cycle.

Global change is defined as a set of several ongoing processes (i.e. climate change, land use change, population increase) (Steffen et al., 2004) that have a direct impact on humans (human health), food provision and on the natural functioning of the Earth’s system (biodiversity, water and element cycles). In the terrestrial system scarce knowledge is available about the possible consequences of global change on BSi pools’ distribution and properties and the consequent implications for the ecosystem Si-filter.

In this thesis the most relevant effects of global change on the terrestrial BSi pool were studied: the effect of fire, the decrease in abundance of large grazers and the combined effects of land use change and erosion. It was found that burned BSi is more soluble than fresh or unburned BSi; the effect of conversion from forest to cropland decreases the BSi pool in the short-term and erosion increases BSi accumulation and possible storage at bottom-slope positions, but the two effects combined results in a stronger BSi depletion and a larger accumulation; the presence of large grazers on the African savannah controls the Si transport from grasses to the river, that eventually reaches the big lakes.

Moreover, the work carried out studying the effects of the global change challenged the method used to characterize and quantified BSi in soils. A refinement of the methodology used was consequently developed which consists on a better performance of the modeling and a novel calculation of an interval of confidence for each parameter estimated. The script developed is available from: